Although there are various recording media for recording and saving digital audio, images, animations, document files and data files which are created by computer, etc., there is an optical disk as one of the recording media. Especially, DVDs (Digital Versatile Disks) have a high density and large capacity as compared with conventional CDs (Compact Discs), and even in the field of picture recording machines, are spreading as media to replace the currently mainstream VTRs (Video Tape Recorders). Moreover, in recent years, BDs (Blu-ray Disks) that are a next-generation optical disk, which have further enhanced recording density using a blue semiconductor laser, are beginning to spread.
In order to increase the capacity of an optical disk, it is necessary to increase the recording density of information by making an optical spot formed by the light radiated to the optical disk smaller when information is recorded on the optical disk and when the information recorded on the optical disk is reproduced. The optical spot can be made smaller by shortening the wavelength of the laser beam of the light source and enlarging the numerical aperture (NA) of an objective lens. In DVDs, a light source with a wavelength of 660 nm and an objective lens with a numerical aperture (NA) of 0.6 are used. On the other hand, in BDs, a recording density of 5 times the recording density of DVDs is attained by using a blue laser with a wavelength of 405 nm and an objective lens of NA 0.85. Additionally, in these optical disks, in order to perform recording and reproducing of data, an optical information device is required.
Meanwhile, as one of the parts which constitute the optical pickup, there is an optical detector for receiving the reflected light from an optical disk to generate a control signal, a reproduction signal, etc. of the optical pickup. It is necessary to adjust and fix this optical detector to a specified position on an optical axis with high accuracy, and a higher accuracy of adjustment and fixation than the conventional technique is required for an optical pickup which performs recording/reproducing on a higher-density disk. In conventional optical pickups for DVDs and CDs, the method described below was used as a method of fixation and adjustment of the optical detector.
For example, in a method shown in Japanese Patent No. 3663141 as a conventional technique, as shown in FIG. 21, cut-in portions 221a and 221b are formed at both ends of a mounting plate 220 which supports an optical detector 210, convex portions 231a and 231b formed on an optical base 230 are inserted into the cut-in portions 221a and 221b of the mounting plate 220, respectively, and the mounting plate 220 is adjusted in a floating state on the air. After the adjustment is performed with high accuracy and the position is temporarily determined, the mounting plate 220 is fixed to an optical base 230, using photo-curable adhesives, such as UV curable resin.
Here, the convex portions 231a and 231b of the optical base 230 have shapes such that the convex portions stick out from both ends of the mounting base 220, and exposed surfaces of the convex portions 231a and 231b of the optical base 230 and the cut-in portions 221a and 221b of the mounting plate 220 are adhered to each other.